Apparatus for forming a blank for finish forging for a forged crankshaft for a three-cylinder engine and method for manufacturing a forged crankshaft for a three-cylinder engine using the same

An apparatus for forming a blank for finish forging for a forged crankshaft for a three-cylinder engine, the apparatus configured to form, in a process of manufacturing the forged crankshaft, the blank for finish forging to be subjected to finish forging by which a final shape of the forged crankshaft is obtained,

• the apparatus configured to form the blank for finish forging from a preform blank, the preform blank including:
• rough journal portions having an axial length equal to an axial length of journals of the forged crankshaft;
• rough crank pin portions having an axial length equal to an axial length of crank pins of the forged crankshaft;
• and rough crank arm portions having an axial thickness greater than an axial thickness of crank arms of the forged crankshaft,
• among the rough crank pin portion in the preform blank, first and third rough crank pin portions at opposite ends having an amount of eccentricity in a direction perpendicular to an axial direction in the opposite direction to each other, the amount of eccentricity thereof being less than a √3/2 of an amount of eccentricity of the crank pins of the forged crankshaft, a second rough crank pin portion in the center having an amount of eccentricity of zero in the direction perpendicular to the axial direction or having an amount of eccentricity in a direction perpendicular to an eccentric direction of the first and third rough crank pin portions, the amount of eccentricity thereof being equal to the amount of eccentricity of the crank pins of the forged crankshaft,
• the apparatus, comprising:
• reference crank pin die disposed at a location of the second rough crank pin portion, the reference crank pin die configured to be brought into contact with the second rough crank pin portion, the reference crank pin die configured to be constrained from moving axially while being in contact with side surfaces of rough crank arm portions through which the rough crank arm portions connect with the second rough crank pin portion;
• movable crank pin dies disposed at locations of the corresponding first and third rough crank pin portions, the movable crank pin dies configured to be brought into contact with the first and third rough crank pin portions, the movable crank pin dies configured to move axially toward the reference crank pin die and in the direction perpendicular to the axial direction, while being in contact with side surfaces of the rough crank arm portions through which the rough crank arm portions connect with the first and third rough crank pin portions;
• and
• journal dies disposed at locations of the corresponding rough journal portions, the journal dies configured to hold and retain such rough journal portions therebetween in the direction perpendicular to the axial direction, the journal dies configured to move axially toward the reference crank pin die while being in contact with side surfaces of the rough crank arm portions through which the rough crank arm portions connect with such rough journal portions,
• wherein, in a state where the rough journal portions are held and retained by the journal dies, and the rough crank pin portions are contacted by the reference crank pin die and the movable crank pin dies, the journal dies are moved axially and the movable crank pin dies are moved axially and in the direction perpendicular to the axial direction, thereby compressing the rough crank arm portions in the axial direction so as to reduce the thickness thereof to the thickness of the crank arms of the forged crankshaft, and pressing the first and third rough crank pin portions in the direction perpendicular to the axial direction but in the opposite direction to each other, so as to increase the amount of eccentricity thereof to the √3/2 of the amount of eccentricity of the crank pins of the forged crankshaft.